forceValue: make pos mandatory

- Make passing the position to `forceValue` mandatory,
  this way we remember people that the position is
  important for better error messages
- Add pos to all `forceValue` calls

src/libexpr/eval-inline.hh

@@ -53,7 +53,7 @@ void EvalState::forceValue(Value & v, const Pos & pos)
 
 inline void EvalState::forceAttrs(Value & v)
 {
-    forceValue(v);
+    forceValue(v, v.determinePos(noPos));
     if (v.type() != nAttrs)
         throwTypeError("value is %1% while a set was expected", v);
 }
@@ -69,7 +69,7 @@ inline void EvalState::forceAttrs(Value & v, const Pos & pos)
 
 inline void EvalState::forceList(Value & v)
 {
-    forceValue(v);
+    forceValue(v, v.determinePos(noPos));
     if (!v.isList())
         throwTypeError("value is %1% while a list was expected", v);
 }